This application is a continuation of U.S. patent application Ser. No. 09/797,458, filed Mar. 1, 2001 by the same inventor, now U.S. Pat. No. 6,604,175, entitled “Improved Data Cache and Method of Storing Data By Assigning Each Independently Cached Area In The Cache To Store Data Associated With One Item.”
1. Field of the Invention
The present invention relates to storing and retrieving data. Specifically, the present invention relates to storing data in a cache and retrieving data from the cache.
2. Description of the Related Art
In computer graphics, existing texture-rendering techniques map a pixel on a screen (typically using screen coordinates (x, y)) to a polygon, such as a triangle, on a surface in a viewing plane (typically using geometric or surface coordinates (s, t)). The polygon is rasterized into a plurality of smaller pieces called fragments. Each polygon may have information, such as color and/or a normal vector, associated with each vertex of the polygon. To assign a texture (i.e., a color pattern or image, either digitized or synthesized) to a fragment, the fragment is mapped onto a texture map (typically using texture coordinates (u, v)). A texture map represents a type of image, such as stripes, checkerboards, or complex patterns that may characterize natural materials. Texture maps are stored in a texture memory. A texture map comprises a plurality of texels. A texel is the smallest graphical element in a 2-D texture map used to render a 3-D object. A texel represents a single color combination at a specific position in the texture map.
Each texture map has a plurality of associated MIP (multum in parvo) maps, which are abbreviated versions of a full texture map. One of the MIP maps may be selected to provide a suitable resolution for the fragment of the polygon being rasterized. Several techniques exist to interpolate the desired color information from one or more MIP levels. These texel selection techniques are known technology. The final texture color derived from the selected MIP map is applied onto the fragment. The applied texture may be blended with a color already associated with the fragment or polygon.
In a traditional graphics rendering pipeline/architecture, a texturing unit will access a texture memory via a texture cache. This traditional architecture treats the texture cache as a single large cache or lookup table created from most of the memory available in the texture cache. A texture memory controller passes new texel data packets from all the texture maps to the single texture cache. Any texel data from any texture map may overwrite texel entries from other maps. There are no provisions for dealing with texel data packets that are frequently re-used compared to texel data packets that are used only intermittently or infrequently. A frequently re-used texel data packet may be written over, reloaded again, written over and then reloaded again repeatedly. The operation of having a single cache handle texel data from many texture maps is inefficient.